1. Field of the Invention
The present invention relates to an IC socket structure which is used for a surface-mount type of IC package.
2. Description of the Related Art
A conventional IC socket structure which is used for a surface-mount type of IC package consists of an arrangement such as that shown in FIG. 4.
As illustrated, a peripheral circuit 5 which is associated with an IC package 2 to be used is arranged on one or both sides of a printed board 4, and the IC package 2 is mounted to an IC socket 3a. When a lid 3b for the IC socket 3a is closed, the lid 3b and the IC socket 3a are locked together by the engagement between a lever 3e and a claw portion of the IC socket 3a. FIG. 5 is a cross section showing this locked state. Leads 2a of the IC package 2 on each side are pressed in contact with corresponding contact springs 3c of the IC socket 3a by projections 3d of the lid 3b, whereby the electrical conduction between the IC package 2 and the peripheral circuit 5 is assured.
However, the above-described conventional art has a number of problems. For example, signal paths extending from the respective leads (pins) 2a of the IC package 2 to the peripheral circuit 5 are excessively long and the signal paths of adjacent pins run in parallel over long distances and with narrow spacings, so that parasitic capacitance becomes large. As a result, if the operating frequency of the packaged IC is increased, signal interference or waveform distortion will occur and the IC may not operate normally. In the worst case, the IC may oscillate. The above-described problem has become increasingly serious in a recent trend toward an increase in the number of pins of an IC package and a reduction in pin-to-pin pitch.
If a method of soldering the IC package 2 to the printed board 4 is used instead of the IC socket 3a , the signal paths can be shortened but the IC package 2 becomes extremely difficult to replace with another IC package. In addition, during replacement, since the printed board 4 is subjected to repetitions of heating and cooling, lands for bearing the leads 2a of the IC package 2 deteriorate and the durability of the printed board 4 is impaired.